Efforts in the design of communication systems generally focus on improving performance, reducing cost or a combination thereof. One area of increasing interest relates to conversion of signals, such as from analog-to-digital or digital-to-analog. As communications systems become increasingly complex, increased dynamic range and increased resolution is required in the signal conversion process. The expense of signal conversion components increases dramatically with an increase in dynamic range and resolution of the converter.
Dynamic range describes the range of the input signal levels that can be reliably measured simultaneously and in particularly the ability of a converter to accurately measure small signals in the presence of large signals. The range of signal amplitudes (or signal strengths) a converter can resolve is typically expressed in decibels. A converter with a dynamic range of 60 dB means that it can resolve signals in the range in amplitude or power from x to 1000x. Dynamic range is important in communication applications where signal strengths vary dramatically. For example, if an analog-to-digital converter (ADC), of a particular dynamic range, receives a signal that is too large, the ADC will over-range the ADC input. The signal may be clipped or become non-sensible. If the same ADC receives a signal that is too small, the signal will get lost in the quantization noise of the converter.
The dynamic range of signal conversion components has an upper bound that is limited by the system full scale signal (e.g., peak levels), and a lower bound that is limited by two independent error signals: system noise floor and spurious signals. The system noise floor is composed of several factors including component (e.g., amplifier) voltage or current noise and quantization noise. The converted signal is equal to the input signal plus system noise. The main source of spurious signals is non-linearities in components such as mixers, amplifiers, and data converters. They can have a higher amplitude than noise and may be added to the wanted signals, contaminate nearby channels, or appear as out-of-band emissions.